Multi-zone air handling systems and methods with variable speed fan

ABSTRACT

An air handling system for supplying one or more zones with airflow. The air handling system generally includes a cold air damper, a hot air damper, a fan, and a controller. The cold air damper is associated with the one or more zones, and is movable between an open position and a closed position. The hot air damper is also associated with the one or more zones, and is movable between an open position and a closed position. The fan is positioned upstream of the cold air damper and the hot air damper and operates at varying speeds to generate the airflow for the one or more zones. The controller modulates the speed of the fan to maintain the cold air damper in an approximately fully open position or an approximately fully closed position.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application Ser. No. 60/701,599, filed Jul. 22, 2005, and U.S. Provisional Patent Application Ser. No. 60/701,595, filed Jul. 22, 2005, the entire contents of both of which are incorporated herein by reference.

FIELD

Embodiments of the invention relate to air handling units.

BACKGROUND

Air handling units (“AHUs”) or heating, ventilation, and air conditioning (“HVAC”) units can be used to regulate temperature, ventilation, and humidity levels of structures of various sizes. AHUs are often employed in a variety of commercial and industrial buildings to ensure the physical comfort of occupants.

SUMMARY

In one embodiment, an air handling system for supplying one or more zones with airflow includes a cold air damper, a hot air damper, a fan, and a controller. The cold air damper is associated with the one or more zones, and is movable between an open position and a closed position. The hot air damper is also associated with the one or more zones, and is movable between an open position and a closed position. The fan is positioned upstream of the cold air damper and the hot air damper and operates at varying speeds to generate the airflow for the one or more zones. The controller modulates the speed of the fan to maintain the cold air damper in an approximately fully open position or fully closed position.

In another embodiment, a method of supplying one or more zones with airflow includes generating airflow with a variable speed fan and routing the generated airflow to a cold air pathway and a hot air pathway. The cold air pathway includes a cold air damper movable between an approximately fully open position and an approximately fully closed position. The hot air pathway includes a hot air damper movable between an open position and a closed position. The method also includes modulating the speed of the fan to maintain the cold air damper in one of the approximately fully open position and the approximately fully closed position.

In another embodiment, an air handling system that supplies airflow to one or more zones includes a variable speed drive and a controller. The variable speed drive turns a fan to generate the airflow for the one or more zones. The controller modulates the speed at which the variable speed drive turns the fan based at least partially on a temperature of the one or more zones. The controller also maintains a cold air damper of the system in an approximately fully open position or an approximately fully closed position.

Other aspects will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of an exemplary air handling system.

FIG. 2 illustrates another block diagram of an exemplary air handling system.

FIG. 3 illustrates yet another block diagram of an exemplary air handling system.

FIG. 4 illustrates an exemplary process for supplying one or more zones with airflow.

FIG. 5 illustrates an exemplary process for controlling outside air entry and an economizer.

FIG. 6 illustrates an exemplary process for controlling a variable speed drive.

FIG. 7 illustrates another exemplary process for controlling a variable speed drive.

FIG. 8 illustrates an exemplary process for controlling the temperature of a cold deck.

FIG. 9 illustrates an exemplary process for controlling the temperature of a hot deck.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.

FIG. 1 illustrates an exemplary air handling system 100 according to an embodiment of the invention. The air handling system 100 generally includes a fan 105 that is driven by a variable speed drive (“VSD”) 110, a plurality of cold air dampers 115, a plurality of hot air dampers 120, and a plurality of zones 125. The air handling system 100 also includes a controller 130. The air handling system 100 can route airflow 135 from the fan 105 to the plurality of zones 125, as described in greater detail below. In other embodiments, the air handling system 100 may have more or fewer cold air dampers 115, hot air dampers 120, and zones 125 than those shown. Additionally, the VSD may also be referred to as a variable frequency drive (“VFD”).

The fan 105 and VSD 110 are used to generate the airflow 135. For example, the fan 105 is turned in accordance with control signals from the VSD 110, and as the fan 105 turns, it creates the airflow 135. As such, the VSD 110 has the ability to decrease or increase the speed of the fan 110, which consequently reduces or increases the amount of airflow 135.

The cold air dampers 115 and hot air dampers 120 control the amount of the airflow 135 that is allowed to flow to the zones 125. For example, the cold air dampers 115 and hot air dampers 120 include one or more movable elements or partitions which can be moved between a fully open position and a fully closed position. When the cold air dampers 115 and the hot air dampers 120 are in the fully open position, substantially all of the airflow 135 is allowed to pass to the zones 125. Conversely, when the cold air dampers 115 and the hot air dampers 120 are in the fully closed position, none, or relatively little, of the airflow 125 is allowed to pass to the zones 125. Generally, as described in greater detail with respect to FIG. 2, the cold air dampers 115 are associated with a cold air deck, which cools the airflow 135 prior to the airflow reaching the zones 125. Additionally, the hot air dampers 120 are generally associated with a hot air deck, which heats the airflow 135 prior to the airflow reaching the zones 125.

The zones 125 are the areas to which the airflow 135 is routed. In some embodiments, such as, for example, a relatively large commercial or industrial structure, the zones 125 can include one or more rooms within the structure. Alternatively, the zones 125 may include one or more entire floors of the structure. The size, shape, and number of zones 125 depend on the size and design of the structure, as well as the capabilities of the air handling system 100.

The controller 130 provides the VSD 110 with a control signal that is used by the VSD 110 to modulate the speed of the fan 105. Generally, the controller 130 can be a suitable electronic device, such as, for example, a programmable logic controller (“PLC”), a personal computer (“PC”), and/or other industrial or personal computing device. As such, the controller 130 may include both hardware and software components, and is meant to broadly encompass the combination of such components. In order to communicate with the VSD 110, the controller 130 is linked to the VSD via hardwired or wireless connections. Additionally, in order to perform functions (e.g., generating VSD control signals, transmitting signals, etc.), the controller 130 includes a set of commands and/or parameters, or a program. The set of commands can be stored, accessed, and/or changed, and can be created using a variety of suitable computer programming languages (e.g., ladder logic, C++, etc.).

In the embodiment shown in FIG. 1, the controller 130 is remote or separate from the VSD 110. However, in other embodiments, the VSD 110 may include an integrated control system (e.g., a dedicated controller integrated with the drive). In such embodiments, the functions of the controller 130 may be integrated into the VSD 110. Additionally, as described in greater detail with respect to FIG. 2, the controller 130 may be in communication with, or linked to, multiple other components of the air handling system 100.

FIG. 2 illustrates another exemplary air handling system 200 according to an embodiment of the invention. The air handling system 200 includes a plurality of mechanical components (e.g., dampers, valves, ductwork, etc.), as well as a plurality of electrical components (e.g., temperature sensors, relative humidity sensors, etc.), which are described in greater detail below. However, it should be noted that the mechanical and electrical component groupings are broad generalizations meant to facilitate the description of the overall air handling system 200. Thus, components described as “mechanical” components may also include associated electrical components (e.g., a damper that is moved by an associated electrical motor), and vice versa.

The mechanical components of the air handling system 200 can be generally split into three sections, each section having its own set of components. For example, an economizer section 203 includes an outside air duct 206, an outside air damper 209, a return air duct 212, a return air damper 215, a release air duct 218, a release air damper 221, a mixed air duct 222, and a supply fan 224. A heating and cooling section 227 includes a cold deck 230 having a cold deck valve 233 and an associated cold air duct 236, and a hot deck 239 having a hot deck valve 242 and an associated hot air duct 245. A zone section 248 includes a plurality of cold air dampers 251, a plurality of hot air dampers 254, zone air ductwork 257, and a plurality of zones 260. Additionally, in some embodiments, the cold air dampers 251 and the hot air dampers 254 have an associated actuator 261. Each of the three sections is described in greater detail below.

The economizer section 203 generally controls the amount of airflow that enters the air handling system 200, the amount of airflow that is returned or recycled through the air handling system 200, and the amount of air that is allowed to be released from or exit the air handling system 200. For example, the outside air duct 206 provides a conduit for airflow to enter the air handling system 200. The outside air damper 209 can be moved from a fully open position to a fully closed position to allow varying amounts of airflow to flow through the outside air duct 209. The return air duct 212 and the return air damper 215, and the release air duct 218 and the release air damper 221, control the airflow in a similar fashion. In some embodiments, the outside air damper 209, the return air damper 215, and the release air damper 221 are linked such that repositioning one of the dampers also causes the other dampers to be repositioned. For example, if the return air damper 215 is positioned approximately 80% open (e.g., 80% of the airflow is recycled or re-circulated), the outside air damper 209 and the release air damper 221 may be positioned 20% open (e.g., 20% of the airflow is allowed to enter from outside, while 20% of the airflow is allowed to be released). Correspondingly, if the return air damper 215 is positioned approximately 90% open (e.g., 90% of the airflow is recycled or re-circulated), the outside air damper 209 and the release air damper 221 may be positioned 10% open (e.g., 10% of the airflow is allowed to enter from outside, while 10% of the airflow is allowed to be released). The mixed air duct 222 provides a conduit for airflow from the outside air damper 209 and the return air damper 215 to mix and be routed to other components of the air handling system 200. In some embodiments, the outside air damper 209, the return air damper 215, and the release air damper 221 are actuated or moved by a damper actuator (e.g., an electric motor, a hydraulic motor, etc.). The supply fan 224 is positioned downstream of the outside air damper 209 and the return air damper 215, and provides the force required to move the airflow through the air handling system 200 at a desired speed. In some embodiments, the speed at which the fan 224 turns is variable, as described in greater detail below.

The heating and cooling section 227 is generally responsible for heating and cooling the airflow of the air handling system 200. For example, the cold deck 230 cools the airflow using one or more cold water coils, or another suitable mechanism, prior to the airflow being routed through the cold air duct 236. The temperature of the cold water coils of the cold deck 230 is controlled using the cold deck valve 233, which allows more or less water to pass through the cold water coils. Thus, by modulating the position of the cold deck valve 233, the temperature of the airflow is effectively controlled. In a similar manner, the hot deck 239 heats the airflow using one or more hot water coils, or another suitable mechanism, prior to the airflow being routed through the hot air duct 245. The temperature of the hot water coils of the hot deck 239 is controlled using the hot deck valve 242. Thus, by modulating the position of the hot deck valve 242, the temperature of the airflow is effectively controlled.

The zone section 248 is generally responsible for mixing the airflow from the cold air duct 236 and the airflow from the hot air duct 245, and routing that mixed airflow to the zones 260. In the embodiment shown in FIG. 2, each zone 260 is supplied with airflow by a single cold air damper 251 and a single hot air damper 254 (e.g., a “damper pair”). Thus, the mixed airflow can be provided to the zones 260 by modulating the respective positions of the cold air dampers 251 and the hot air dampers 254 associated with each zone 260, and routing the airflow from the cold air dampers 251 and the hot air dampers 254 through the zone air ductwork 257. In some embodiments, each damper pair is coupled, or otherwise linked, such that as the cold air damper 251 closes, the hot air damper 254 opens, and vice versa. Thus, if the cold air damper 251 of a damper pair is positioned in a fully open (or approximately fully open) position, the hot air damper 254 of the damper pair is positioned in a fully closed (or approximately fully closed) position. As previously described, in some embodiments, the cold air dampers 251 and the hot air dampers 254 are actuated or moved by the associated damper actuators 261. These damper actuators 261 may be electronically controlled, as described in greater detail below.

The three sections detailed above also include electrical components. For example, the electrical components of the economizer section 203 include an outside air temperature sensor 263, a return air temperature sensor 266, a mixed air temperature sensor 269, a return air relative humidity sensor 272, and a VSD 275. The electrical components of the heating and cooling section 227 include a cold supply air temperature sensor 281 and a hot supply air temperature sensor 278. The electrical components of the zone section 248 include zone air temperature sensors 284. The air handling system 200 also includes a controller 287, which is not associated with any particular section of the air handling system 200.

The electrical components associated with the economizer section 203 generally measure the temperature of the outside air, return air, and mixed air, and the relative humidity of the return air. Additionally, the VSD 275 controls the speed of the fan 224, which affects the amount of airflow that is moved through the air handling system 200. In the embodiment shown in FIG. 2, the outside air temperature sensor 263 is positioned within or proximate to the outside air duct 206, and generates a signal that is indicative of the temperature of the airflow in the outside air duct 206. Similarly, the return air temperature sensor 266 and the mixed air temperature sensor 269 are positioned within the return air duct 212 and the mixed air duct 222, respectively, and generate signals that are indicative of the temperature of the airflow in the return air duct 212 and the temperature of the airflow in the mixed air duct 222, respectively. Additionally, the return air relative humidity sensor 272 is positioned within the return air duct 212, and generates a signal indicative of the relative humidity of the return airflow (e.g., the airflow that has been circulated through the zones 260). The cold supply air temperature sensor 281 and the hot supply air temperature sensor 278 associated with the heating and cooling section 227 generate signals indicative of the temperature of the airflow in the cold air duct 236 and the airflow in the hot air duct 245, respectively. The zone air temperature sensors 284 associated with the zone section 248 generate signals indicative of the temperature of the zones 260. In some embodiments, the zone air temperature sensors 284 are incorporated or integrated into a thermostat device. In such embodiments, the zone air temperature sensors 284 may also generate or otherwise provide temperature set point signals, which indicate desired heating temperatures and/or desired cooling temperatures (e.g., a heating temperature of 70 degrees Fahrenheit and a cooling temperature of 72 degrees Fahrenheit). The signals generated by the described sensors may be provided to the controller 287, as described in greater detail below.

Generally, the controller 287 receives data signals from and transmits control signals to (e.g., is in communication with) many of the mechanical and electrical components of the air handling system 200. For example, in the embodiment shown in FIG. 2, the controller 287 receives data signals from the outside air temperature sensor 263, the return air temperature sensor 266, the mixed air temperature sensor 269, the cold supply air temperature sensor 281, the hot supply air temperature sensor 278, and the zone air temperature sensors 284. Additionally, the controller 287 transmits control signals to the damper actuators of the outside air damper 209, the return air damper 215, and the release air damper 221. The controller 287 also transmits control signals to the cold deck valve 233, the hot deck valve 242, and the damper actuators 261 associated with the cold air dampers 251 and the hot air dampers 254. In some embodiments, the controller 287 also transmits a control signal to the VSD 275, which, in turn, transmits a control signal to the fan 224. These signals are utilized and generated by the controller 287 according to one or more processes or programs, such as, for example, the processes described with respect to FIGS. 4-9, to carry out a plurality of air handling system functions. As such, similar to the controller 130 (FIG. 1), the controller 287 can be a suitable electronic device, such as, for example, a programmable logic controller (“PLC”), a personal computer (“PC”), and/or other industrial or personal computing device that includes both hardware and software components that is capable of carrying out such processes and programs.

FIG. 3 illustrates yet another exemplary air handling system 300 according to an embodiment of the invention. Many of the components of the air handling system 300 are similar to the components of the air handling system 200 (FIG. 2) (similar components of the systems are numbered accordingly, for example, “2xx” is changed to “3xx”). Thus, not all of the components of the air handling system 300 are described in detail. Rather, several differences between the air handling system 300 and the air handling system 200 are described. The air handling system 300 and the air handling system 200 may include other differences that are not specifically addressed herein.

In addition to the components described in the air handling system 200 shown in FIG. 2, the air handling system 300 of FIG. 3 includes a neutral supply air duct 390 and a plurality of neutral air dampers 393. Thus, the airflow being generated by a fan 324 is split into three ducts including a cold supply air duct 336, a hot supply air duct 345, and the neutral supply air duct 390. Additionally, each zone 360 includes four associated dampers, or two separate damper pairs. For example, in the embodiment shown in FIG. 3, each of the zones 360 includes a damper pair having a hot air damper 354 and a neutral air damper 393, and a damper pair having a cold air damper 351 and a neutral air damper 393. Generally, the two dampers of a damper pair are linked so that the dampers open and close together. For example, if the hot air damper 354 closes, the corresponding neutral air damper 393 also closes. However, in some embodiments, the hot air damper 354 and the cold air damper 351 of the separate damper pairs are also linked, such that as a hot air damper 354 and a neutral air damper 393 of one damper pair closes, the cold air damper 351 and the neutral air damper 393 of the related damper pair opens, and vice versa. As such, when the cold air damper 351 and corresponding neutral air damper 393 of a particular zone 360 are in a fully closed (or approximately fully closed) position, the hot air damper 354 and corresponding neutral air damper 393 of that zone 360 are in a fully open (or approximately fully open) position.

Introducing neutral air into the airflow of the air handling system 300 may reduce cost, because not all of the airflow has to be heated or cooled. However, introducing neutral air into the airflow of the air handling system 300 may also affect the characteristics of the airflow (e.g., the relative humidity of the airflow). As such, the controller 387 of the air handling system 300 may have the capability to adjust components of the air handling system 300 to account for the changing characteristics of the airflow (e.g., mechanisms and/or processes that modulate the temperature of a cold deck 330).

FIGS. 4-9 describe processes that can be used to control the components of an air handling system, such as, for example, the air handling systems described with respect to FIGS. 1-3. For example, the processes described in FIGS. 4-9 may be carried out by the controller 287 and/or other components shown in FIG. 2. However, it should be noted that the processes shown in FIGS. 4-9 can be adapted for use with a variety of air handling systems, and are not limited in implementation to controlling the components of the air handling system 200.

FIG. 4 illustrates an exemplary process 400 for supplying one or more zones with airflow according to an embodiment of the invention. The process 400 begins by generating airflow with a variable speed fan (step 405). For example, airflow can be generated using the fan 224 and the VSD 275. The next step in the process is to route the generated airflow to a cold air pathway and a hot air pathway, such as the cold supply air duct 236 and the hot supply air duct 245 (step 410). The final step in the process 400 is to modulate the speed of the fan 224 according to the position of a damper, such as the cold air damper 251 or the hot air damper 254 (step 415). For example, as described with respect to FIGS. 6 and 8-9, the position of a damper may affect how quickly or slowly the fan 224 is required to turn.

FIG. 5 illustrates an exemplary process 500 for controlling the amount of outside air that is allowed to enter the air handling system 200, as well as the damper positions of the economizer section 203 (e.g., the outside air damper 209, the return air damper 215, and the release air damper 221). The first step in the process is to check whether the outside air temperature is higher than a high limit temperature of the economizer section 203 or if the outside air temperature is lower than a low limit temperature of the economizer section 203 (step 505). This step can be completed, for example, using data from the outside air temperature sensor 263. In one embodiment, the low limit temperature of the economizer section 203 is approximately 10 degrees Fahrenheit, and the high limit temperature of the economizer section 203 is approximately 65 degrees Fahrenheit. If the outside air temperature is not within an acceptable economizer range, the air handling system 200 allows a minimum amount of outside air into the air handling system 200 (step 510). This may cause the controller 287 to at least partially close the outside air damper 209, and, correspondingly, open the return air damper 215 to allow more of the airflow to be re-circulated. Re-circulating airflow through the air handling system 200 can help reduce operating costs, because there is relatively little new airflow (e.g., airflow from outside) to be heated or cooled by the hot deck 239 and the cold deck 230, respectively.

If the outside air temperature is within the temperature range of the economizer section 203 (e.g., the outside air temperature is between the high temperature limit and the low temperature limit), the next step in the process 400 is to evaluate a weighted damper position for the zones 260 of the air handling system (step 515). In the embodiment shown in FIG. 4, the weighted damper position of the cold air damper 251 is calculated. In other embodiments, however, the weighted damper position can be calculated for the hot air damper 254. The weighted damper position can be calculated for the zones 260 of the air handling system 200 using the following equation: x=Σ _(i=1) ^(n) y _(i)β_(i) In the equation above, y_(i) represents a damper position command that ranges from 0 to 1 for zone i. A damper position command of 0 corresponds to the cold air damper 251 being fully open, while a damper position command of 1 corresponds to the cold air damper 251 being fully closed. Additionally, the variable β_(i) represents a ratio of a design airflow value of zone i to a total design airflow of the air handling system 200. Thus, the variable β_(i) changes from one zone 260 to another if the zones 260 are different sizes (e.g., the variable β_(i) gives more weight to larger zones).

The weighted damper position calculated in step 515 can then be used to set a return air damper position by comparing the weighted damper position of the zones 260 to 0.6 (step 520). For example, the position of the return air damper 215 can be adjusted according to the current heating or cooling condition for the zones 260 (i.e., the weighted damper position), in order to control how much of the outside air enters the air handling system 200. Generally, a weighted damper position that is less than 0.6 indicates that the cold air dampers 251 are more open than closed (i.e., the zones 260 are being cooled). As such, a mixed air temperature set point (e.g., a set point corresponding to the air temperature measured by the mixed air temperature sensor 269) is set to a cold air temperature set point (e.g., 55 degrees Fahrenheit), and the return air damper 215 is modulated to maintain the cold air temperature set point (step 525). For example, the return air damper 215 is positioned to re-circulate enough of the airflow to maintain the cold air temperature set point (as measured by the mixed air temperature sensor 269), while drawing any remaining required airflow from the outside air. Modulating the return air damper 215 in this way can reduce costs, because a minimal amount of outside air is required to be cooled by the cold deck 230 prior to being routed to the zones 260.

Generally, a weighted damper position of more than 0.6 indicates that the cold air dampers 251 are more closed than open (e.g., the zones 260 are being heated). As such, if the weighted damper position is greater than 0.6, the mixed air temperature set point is set to a hot air temperature set point (e.g., 70 degrees Fahrenheit), and the return air damper 215 is positioned to re-circulate enough of the airflow to maintain the hot air temperature set point (as measured by the mixed air temperature sensor 269), while drawing any remaining required airflow from the outside air. Modulating the return air damper 215 in this way can reduce costs, because a minimal amount of outside air is required to be heated by the hot deck 239 prior to being routed to the zones 260.

In other embodiments, the positions of the economizer dampers (i.e., the outside air damper 209, the return air damper 215, and the release air damper 221) can be controlled differently. For example, the weighted damper position may be calculated differently, or compared to a value other than 0.6. Additionally, the cold air temperature set point and the hot air temperature set point are variable, and may depend on the heating or cooling load of the structure.

FIG. 6 illustrates an exemplary process 600 for controlling a VSD according to an embodiment of the invention. The process 600 can be used, for example, to modulate the speed of the VSD 275 (FIG. 2) using control signals from the controller 287 to ensure that at least one of the cold air dampers 251 is in a fully closed position or a fully open position. By maintaining at least one of the cold air dampers 251 in a fully closed position or a fully open position, resistance in the air handling system 200 is reduced, because mixing of cold airflow from the cold supply air duct 236 and hot airflow from the hot supply air duct 245 is minimized. Additionally, costs may be reduced because simultaneous heating of airflow and cooling of airflow is minimized. As previously described, the zone damper positions (i.e., the cold air dampers 251 and the hot air dampers 254) can be evaluated on a scale of 0 to 1, with 0 being the fully open position and 1 being the fully closed position. Similarly, the controller 287 can transmit control signals to the damper actuators 261 based on the 0 to 1 scale. For example, when the controller 287 transmits a control signal of 0.05 to the damper actuators 261, the damper actuators move the cold air dampers 251 to an approximately fully open position and the hot air dampers 254 to an approximately fully closed position. Correspondingly, when the controller 287 transmits a control signal of 0.95 to the damper actuators 261, the damper actuators 261 move the cold air dampers 251 to an approximately fully closed position and the hot air dampers 254 to an approximately fully open position. The commands of 0.05 and 0.95 are used to ensure that the damper actuators 261 do not stress the dampers by opening them too far or closing them too tightly; however, other similar commands can be used (e.g., 0.03 and 0.97).

The process 600 begins by measuring the speed of the fan 224 (step 605) and measuring the position of the cold air dampers 251 (step 610). In some embodiments, the controller 287 continually receives fan speed data and damper position data. In such embodiments, steps 605 and 610 can be omitted. The next step in the process 600 is to check if a maximum damper command is equal to one, or a minimum damper command is equal to zero (step 615). For example, the highest or lowest damper commands that are transmitted to the damper actuators 261 by the controller 287 are compared to one and zero, respectively. If the maximum damper command is one or the minimum damper command is zero, the fan speed is increased (step 620). This can be completed, for example, by the controller 287 transmitting a control signal to the VSD 275 to increase the speed of the fan 224.

If, however, the maximum damper command is not one and the minimum damper command is not zero, the next step in the process 600 is to check if the maximum damper command is less than 0.95, if the minimum damper command is higher than 0.05, and if the VFD is higher than the minimum VFD speed (step 625). If the three conditions set forth in step 625 are true, the fan speed is decreased (step 630). If the three conditions set forth in step 625 are not true, the current fan speed is maintained (step 635). The manner in which, and amount by which, the fan speed is increased and decreased during the process 600 are variable, and can depend on the size, type, and configuration of the air handling system 200.

FIG. 7 illustrates another exemplary process 700 for controlling a variable speed drive according to an embodiment of the invention. Generally, the process 700 is used to modulate the speed of the VSD 275 (and the associated fan 224) to ensure that at least one of the temperatures of the zones 260 is equal to a heating set point minus a control band or a cooling set point plus a control band, as described in greater detail below. The first step of the process 700 is to measure the temperature of each of the zones 260 (step 705). The next step of the process 700 is to check if the temperature of at least one of the zones 260 is greater than a heating set point (e.g., 69 degrees Fahrenheit) minus a control band (e.g., approximately 1 to 2 degrees Fahrenheit) (step 710). If the temperature of at least one of the zones 260 is not greater than the heating set point minus the control band, the fan speed is increased (step 715). If the temperature of at least one of the zones is greater than the heating set point minus the control band, the next step in the process 700 is to check if the temperature of at least one of the zones is less than a cooling set point (e.g., 71 degrees Fahrenheit) plus the control band (step 720). If the temperature of at least one of the zones 260 is not less than the cooling set point plus the control band, the fan speed is increased (step 715).

If, however, the temperature of at least one of the zones 260 is less than the cooling set point plus the control band, the next step in the process 700 is to check if the fan speed is greater than a minimum fan speed limit (step 725). The minimum fan speed limit can be set, for example, as a parameter within the controller 287 and/or the VSD 275 to ensure that the fan 224 continues to force air through the air handling system 200 at a minimum rate. If the fan speed has not yet reached the minimum fan speed limit, the fan speed is decreased (step 730). If the fan speed has already reached the minimum fan speed limit, the fan speed remains at the minimum fan speed limit (step 735). In other embodiments, the process 700 can be carried out differently. For example, in one embodiment, the steps 710 and 720 can be transposed.

FIG. 8 illustrates an exemplary process 800 for controlling the temperature of a cold deck according to an embodiment of the invention. The process 800 can be used, for example, to control the temperature of the cold deck 230 using the cold deck valve 233, which can affect the relative humidity ratio of the airflow in the air handling system 200. The first step in the process 800 is to check if a return air relative humidity ratio is greater than 60%. The relative humidity of the return airflow can be measured using the return air relative humidity sensor 272. If the return air relative humidity ratio is higher than 60%, the cold deck temperature is set to 55 degrees Fahrenheit (step 810). If, however, the return air relative humidity ratio is lower than 60%, the next step in the process 800 is to check if the return air relative humidity ratio is less than 55%, the minimum air damper command (as described, for example, with respect to FIG. 6) is greater than 0.05, and the speed of the VSD 275 is greater than the minimum VSD speed (step 815). If the conditions set forth in step 815 are true, the cold deck set point is increased (step 820). Increasing the cold deck set point can cause the cold deck valve 233 to raise the temperature of the cold deck by decreasing the cold water flow. If the conditions set forth in step 815 are not true, the next step in the process 800 is to check if the minimum damper command is less than 0.05 and the speed of the VSD 275 is greater than the minimum VSD speed (step 825). If the conditions set forth in step 825 are true, the cold deck set point is decreased (step 830). Decreasing the cold deck set point can cause the cold deck valve 233 to lower the cold deck temperature by increasing the cold water flow.

FIG. 9 illustrates an exemplary process 900 for controlling the temperature of a hot deck according to an embodiment of the invention. The process 900 can be used, for example, to control the temperature of the hot deck 239 using the hot deck valve 242, which can affect the temperature of the airflow being routed through the hot supply air duct 245 to the zones 260. The first step in the process 900 is to set a high temperature limit for the hot deck 239 (step 905). Typically, the hot deck temperature should not exceed 120 degrees Fahrenheit. Additionally, the high limit of the hot deck temperature may range from 120 degrees Fahrenheit to 80 degrees Fahrenheit, depending on the outside air temperature. For example, if the outside air temperature is 0 degrees Fahrenheit, the high limit of the hot deck 239 may be 120 degrees Fahrenheit (e.g., the outside air requires relatively considerable heating). Alternatively, if the outside air temperature is 80 degrees Fahrenheit, the high limit of the hot deck 239 may also be 80 degrees Fahrenheit (e.g., the outside air requires little heating). If a hot deck temperature is requested that is greater than the high limit of the hot deck 239, the controller 287 may issue an alarm and/or other warning, indicating a possible malfunction or system fault.

The next step in the process 900 is to check if the speed of the VSD 275 is less than the minimum VSD speed and the maximum damper position command is less than 0.95 (step 910). If the conditions set forth in step 910 are true, the hot deck temperature set point is decreased (step 915). Decreasing the hot deck temperature set point can cause the controller 287 to send a control signal to the hot deck control valve 242 to reduce the amount of heated water that flows through the hot deck 239. If the conditions set forth in step 910 are not true, the next step of the process 900 is to check if the speed of the VSD 275 is greater than the minimum VSD speed and the maximum damper position command is greater than 0.95 (step 920). If the conditions set forth in step 920 are true, the hot deck temperature set point is increased (step 925). Increasing the hot deck temperature set point can cause the controller 287 to send a control signal to the hot deck control valve 242 to increase the amount of heated water that flows through the hot deck 239. If the conditions set forth in step 920 are not true, the next step in the process 900 is to check if the hot deck temperature is greater than a maximum hot deck temperature set point of the hot deck 239 (i.e., the high limit of the hot deck 239) (step 930). If the hot deck temperature is greater than the maximum hot deck temperature set point, the next step in the process 900 is to maintain the current hot deck temperature (step 935). If the hot deck temperature is not greater than the maximum hot deck temperature set point, the process 900 begins again at step 905.

Each of the processes described in FIGS. 5-9 is illustrated as continually running “control loops.” For example, after an action is completed (e.g., increasing the hot deck temperature set point), the process returns to the first step in the process. However, in some embodiments, the processes need not be completed on a continual basis, and can be completed only as needed. For example, the hot deck temperature set point may only be changed several times a day, rather than on a continual basis.

Various features and advantages of the invention are set forth in the following claims. 

1. An air handling system for supplying one or more zones with airflow, the air handling system comprising: a cold air damper associated with the one or more zones, the cold air damper movable between an open position and a closed position; a hot air damper associated with the one or more zones, the hot air damper movable between an open position and a closed position; a fan positioned upstream of the cold air damper and the hot air damper, the fan configured to operate at varying speeds to generate the airflow for the one or more zones; and a controller configured to modulate the speed of the fan to maintain the cold air damper in an approximately fully open position or an approximately fully closed position.
 2. The air handling system of claim 1, wherein the cold air damper and the hot air damper are linked such that closing the cold air damper opens the hot air damper and opening the cold air damper closes the hot air damper.
 3. The air handling system of claim 1, further comprising a variable speed drive configured to drive the fan.
 4. The air handling system of claim 1, wherein the controller is configured to increase the fan speed when the cold air damper is in the fully open position or the fully closed position.
 5. The air handling system of claim 1, wherein the controller is configured to decrease the fan speed when the cold air damper is positioned between the fully open position and the fully closed position and the fan speed is greater than a predetermined minimum value.
 6. The air handling system of claim 1, further comprising at least one zone temperature sensor associated with the one or more zones and configured to transmit a signal to the controller indicative of a temperature of the one or more zones, and wherein the controller is configured to increase the fan speed to maintain the temperature within a predetermined target temperature band.
 7. The air handling system of claim 6, wherein the controller is configured to decrease the fan speed if the temperature of the one or more zones is within the predetermined target temperature band and the fan speed is higher than a predetermined minimum fan speed value.
 8. The air handling system of claim 1, further comprising at least one neutral air damper associated with the one or more zones.
 9. The air handling system of claim 1, further comprising a cold deck positioned upstream of the cold air damper, and wherein the controller is configured to modulate the temperature of the cold deck based at least partially on the fan speed and the position of the cold air damper.
 10. The air handling system of claim 1, further comprising a hot deck positioned upstream of the hot air damper, and wherein the controller is configured to modulate the temperature of the hot deck based at least partially on the fan speed and the position of the cold air damper.
 11. A method of supplying one or more zones with airflow, the method comprising: generating airflow with a variable speed fan; routing the generated airflow to a cold air pathway and a hot air pathway, the cold air pathway including a cold air damper movable between an approximately fully open position and an approximately fully closed position, the hot air pathway including a hot air damper movable between an open position and a closed position; and modulating the speed of the fan to maintain the cold air damper in one of the approximately fully open position and the approximately fully closed position.
 12. The method of claim 11, further comprising cooling air in the cold air pathway with a cold air deck and heating air in the hot air pathway with a hot air deck.
 13. The method of claim 12, further comprising mixing neutral air with the cold air from the cold air pathway and hot air from the hot air pathway.
 14. The method of claim 12, further comprising controlling the relative humidity of the one or more zones by altering the temperature of the cold air deck.
 15. The method of claim 11, further comprising increasing the fan speed when the cold air damper is in the approximately fully open position or the approximately fully closed position.
 16. The method of claim 11, further comprising decreasing the fan speed when the cold air damper is positioned between the approximately fully open position and the approximately fully closed position and the fan speed is greater than a predetermined minimum fan speed.
 17. An air handling system configured to supply airflow to one or more zones, each zone having an associated cold air damper and an associated hot air damper, the air handling system comprising: a variable speed drive configured to turn a fan to generate the airflow for the one or more zones; and a controller configured to modulate the speed at which the variable speed drive turns the fan based at least partially on a temperature of the one or more zones, and further configured to maintain the cold air damper in an approximately fully open position or an approximately fully closed position.
 18. The air handling system of claim 17, wherein the controller is configured to increase the speed at which the variable speed drive turns the fan when the temperature of the one or more zones is outside a predetermined temperature range.
 19. The air handling system of claim 18, wherein the controller is configured to decrease the speed at which the variable speed drive turns the fan when the temperature of the one or more zones is within a predetermined temperature range and the fan is turning at a greater speed than a predetermined minimum fan speed.
 20. The air handling system of claim 17, wherein each zone includes a neutral air damper and the controller is configured to adjust the speed at which the variable speed drive turns the fan based at least partially on the position of the neutral air damper. 